1. Technical Field of the Invention
The present invention relates in general to the mobile communications field and, in particular, to a method and system for controlling the quality of handovers in a mobile communications system.
2. Description of Related Art
Inter-cell handovers (i.e., from one cell to another) are made in mobile communications systems for various reasons. For example, a mobile station (MS) can be handed over from one cell to another if the radio connection is poor on the original connection. Handovers can also be used for load balancing between cells (e.g., an MS can be moved from a congested cell to a cell with less traffic). However, in many handover situations, the new cell may offer a relatively low carrier-to-interference ratio (C/I) or carrier-to-noise ratio (C/N). Consequently, a handover to such a cell can result in poor speech quality and disrupted calls.
In existing mobile communications systems, there are no mechanisms in place to prevent handovers to cells with a too low C/I or C/N. As such, once a base station controller (BSC) has decided to move an MS from one cell to a new cell, the handover procedure is executed without any attempt to examine beforehand the quality of the radio environment of the new cell. In fact, a standard handover procedure is to perform the handover signalling phase at a safe output power level, in order to ensure a successful handover thereafter. As described below, these drawbacks of existing mobile communications systems in not ensuring the quality of a new cell's radio environment prior to handover are successfully corrected by the present invention.